Auto merge of #45 - danlrobertson:tex_image, r=metajack
Implement copyTexImage2D, copyTexSubImage2D and texSubImage2D Implement copyTexImage2D, copyTexSubImage2D and texSubImage2D and add rules to the `.gitignore` for vim users. Let me know if I missed anything! Blocked by: servo/gleam#80 <!-- Reviewable:start --> --- This change is [<img src="https://reviewable.io/review_button.svg" height="35" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/webrender_traits/45) <!-- Reviewable:end -->